Filter assemblies have for example been employed in a variety of applications including hydraulic systems, fuel systems and engine lubrication systems. Application of filter systems for filtering gaseous media are also known. Such assemblies for example use replaceable filter elements that can be installed on a filter head for filtering fluid flowing between inlet and outlet ports in the filter head. The filter element typically is contained within a filter housing such as a can that can be screwed onto or off of the filter head. In a so-called spin-on filter, the can is discarded along with the filter element. In other arrangements, only the filter element is replaced and the filter housing is reused. During use the filter element may become clogged to the point that is causes a problem in the system, such as inadequate flow to components downstream of the filter, excessive pressure upstream of the filter element, and/or damage to the filter element allowing the accumulated contaminants to flow to components downstream of the filter element. Normally this is avoided by scheduled replacement of the filter element, or after the need of replacement has been brought to the attention of the operator of the system, which may be in the form of an alarm issued by the fluid system for example. It is thus necessary to replace the filter element from time to time.
Filter elements commonly have a wall of a filtration medium and an end cap with an inlet (or outlet) which can be sealed to the head part of the housing to provide a flow path for a fluid stream to be supplied to the interior or space (or to be extracted from the space) within the filter element. The inlet (or outlet) is provided by a port or passage on an end cap of the element. The port may e.g. have an O-ring seal on its external surface which is received in a bore within the housing end cap, in which it is compressed to form a seal. Often, such a filter element has a cylindrical shape. The fluid to be filtered enters the filter assembly via the inlet, the inlet being arranged in such manner that the fluid can distribute along the outer surface of the filter element. The fluid is then forced through the filter element whereby contaminants in the fluid remain captured in the filter element and the filtered fluid is forced to an outlet of the filter assembly. As an alternative, the flow may be in opposite direction; the contaminated fluid entering the filter element axially and then being forced through the filter element thereby flowing substantially radially outward.
Filter assemblies as described can e.g. be applied to filter oil of a lubrication system or an hydraulic system of e.g. a crane. In order to maintain the fluid flowing through the system (i.e. comprising tubing and a filter assembly), a pump is required. This is due to the fact that both the tubing and the filter assembly represent a resistance for the fluid flow. In general, the pump can be driven by an electrical motor or a combustion engine such as diesel engine for example.
In order to gain access to the filter element when it has to be replaced, the head and body parts, if any, of the filter housing can be separated. A concern of known filter assemblies when replacing the filter element is, that some fluid such as for example hydraulic oil or free fluid content in gasses remains in the conduit that is attached to the outlet port of the filter assembly. In case of a filter used for filtering gaseous media, liquid media etcetera, the fluid content could drain out when replacing the filter element. By separating the filter housing from the filter head, this fluid may be spilled, as the filter housing is often still (partly) filled with fluid. Even if the filter housing is drained before removing it from the filter head, some fluid will flow out of the conduit attached to the outlet port due to gravitation. Spilling of fluid, in particular hydraulic fluid, constitutes on the one hand a safety hazard when it is spilled on floors, on the other hand it constitutes an environmental hazard.
In particular filter assemblies used for filtering hydraulic fluids may advantageously be provided with a so-called core element. Such a core element extends along the filter element on that side thereof that is part of the clean part of the fluid system. In other words, the core element is located at the downstream side of the filter element. Due to the nature of the filter element there exists a pressure drop over the filter element. This pressure drop may be substantial, in particular for high-pressure hydraulic systems. The consequence thereof is that also the pressure difference over the filter element may be substantial. Filter elements commonly used in hydraulic systems are not adapted to withstand high pressure differences and will buckle if the pressure difference is too large. The core element provides the required structural strength and is for example made from stainless steel or any other suitable material. In order to reduce costs, the core element is often provided as a separate element of the filter assembly and should normally not be replaced when the filter element is replaced. Hence, when the filter element is replaced the person replacing it must be aware that the core element must be put back in the filter assembly. It has shown in practice that this may easily be forgotten. The core element is than left in the filter element and thrown away with it. In case this is discovered in time, a new core element is placed which increases costs. In case the missing core element is not noticed, the new filter element will collapse with disastrous consequences for the filter assembly. A solution to this concern is proposed in German utility model DE 200 04 431 U, wherein a filter housing is proposed that is provided with a circular wall member in its bottom section extending in longitudinal direction within said filter housing from the bottom part thereof and which can establish a snap coupling with a core element. A concern of this solution is that the filter housing is of a relatively complicated design and thus is relatively expensive, in particular because the filter housing of DE 200 04 431 U has to be made by casting.